${\displaystyle U_{\text{i}}={\displaystyle \underset{r_{\text{a}}\left(\text{C}\right)}{\overset{r_{\text{b}}}{\int }}\left(-\frac{\partial A}{\partial t}+v\times B\right)\cdot \text{d}r}}$

where A and B are respectively a magnetic vector potential and the magnetic flux density at a point of the path, v is the velocity with which that point is moving, r is position vector, and t is time

NOTE – The induced voltage is equal to the time derivative of the linked flux corresponding to the path, with the positive or negative signs according to the convention in IEC 60375.